The present application relates to a method for determining a state of charge of a rechargeable battery.
Determining the state of charge (SOC) and the state of health (SOH) of a rechargeable battery are known as challenging problems regarding modern battery technology. This is particular the case as degradation mechanisms in batteries are complex and a detailed analytical description of the electrochemical processes involved is often not available.
However, knowledge about the state of charge and state of health becomes increasingly important as the number of battery-driven applications is increasing.
This is in particular true as a robust state of charge determination for rechargeable batteries is made even more complicated by highly fluctuating load profiles as well as partial recharge cycles involved. The latter is the case for instance in off-grid applications involving renewable energy generation or in electric vehicle applications, wherein recharging of the battery occurs when energy is available, for example when the sun is out and driving a photovoltaic module or a car recuperates energy when breaking. Furthermore diesel generator running time can be reduced in those off-grid applications, which are mainly powered by renewable energy sources and batteries.
Most state of health algorithms rely on a comparison of measured discharge capacities and rated discharge capacities requiring a robust state of charge determination.
While robust SOC and SOH determination is more easily available for batteries of all types once dedicated hardware for measuring these is not an issue, most applications require cost-sensitive designs of the battery control as well as prohibit any interference of the SOC or SOH measurements with the charging or discharging processes.